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A.J. Mioduszewski, M.P. Rupen (NRAO), R.M. Hjellming (NRAO (deceased))
We summarize the available radio observations of the X-ray transient XTE J0421+560, identifed with the B[e] star CI Camelopardalis. A re-analysis of early data from the Very Large Array (VLA), taking account of the unusually extended structure of the phase calibrator, shows no evidence for the relativistic jets originally reported. The source appears more like a nova than a microquasar, as Very Long Baseline Array (VLBA) images reveal a beautiful expanding and decelerating shell. CI Cam remains however quite unusual: the initial radio emission is synchrotron rather than thermal, and the expansion speed is higher than for normal novae (5000 km/s, for a distance of 5 kpc). The radio flux density has been roughly constant for several years, and is still only slightly resolved by the VLA; at high frequencies it is substantially smaller than an extrapolation of the initial (decelerated) expansion would predict. The long-lived emission has a flat radio spectrum, and is either optically-thick (hence very small scale) synchrotron emission, or thermal emission from a >500 K ionized gas. At ~1 mJy this long-lived emission would not have been seen by any pre-flare observations, and may actually pre-date the explosion which brought the source to our attention.
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Bulletin of the American Astronomical Society, 34, #4
© 2002. The American Astronomical Soceity.